Trolling Paravane Kit (Downrigger)

Has anyone ever used one of these.

I just bought a BLUE-LINE Trolling Paravane Kit for keeping the spoons at a depth whilst trolling.

If anyone knows the thing i'm talking about. what speed and what setting should u have if you want to troll the lure at about 3m deep.

i've got 40lb line.

thanks

4 knots max and the middle setting on the paravane back.